Leptonic cascade around Kerr BHs and the formation of relativistic jets

Relativistic jets from Active Galactic Nuclei (AGN), blazars, quasars and micro-quasars, radio-active galaxies and some other systems host rapidly spinning (Kerr) black holes (BHs). They are powered by Blandford-Znajek mechanism, which converts the BH rotational energy into Poynting flux. This process requires the presence of external magnetic fields brought by accreting gas and highly ionized plasma created {\it in situ}. Thus, plasma production in the so-called ``gap'' region of the BH magnetosphere is crucial for the jets to exist. Here we explored numerically the conditions (the ambient photon field, magnetic field strength, BH spin) needed for the cascade for be efficient, and discuss the properties of the astrophysical systems needed to exhibit powerful jets.